On 12/12/2010 06:08 PM, Abdul Wahid Memon wrote:
Hello everyone I have few questions regarding loop unrolling and the effect of flags (provided at command line) on the execution of passes. Is it possible to do loop unrolling without using -O3, -O2 and -O1? The -Q -O3 --help=optimizers options provides us the list of enabled and disabled optimizations at -O3 level. If I specify -O3 to compile any file then the total number of passes executed are around 182. And If I manually specify all the optimization which are enabled at -O3 (without specifying -O3 actually), we get the total number of passes as 64. So, my question is that why is there a difference of passes between these two cases?
This question is asked on this list just about every month; the manual documents the optimizer options that are controllable via flags at each level, but there are many more optimization behaviors enabled at each level which do not have individual controls.
In other words, it is not possible to manually enable all optimizations that would be enabled when using -O3; it is only possible to enable all of them with -O3 and then disable any that you don't want enabled (which is why the manual documents them).
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